1. Field of the Invention
The present invention relates to an electromagnetic relay and a circuit substrate comprising the same, and in particular, to those for preventing erroneous operation when they are wet by water from condensation or the like.
2. Description of the Related Art
A typical power window (apparatus) provided in a car comprises an electromagnetic relay for normally and reversely rotating a motor for opening or closing the window (pane). The circuit substrate on which the electromagnetic relay is attached may adopt a specific structure for preventing erroneous operation of the motor due to water leakage caused by condensation or the like. For example, a sensor for detecting water leakage is provided in the circuit substrate, and when the sensor detects a leakage, the motor is driven using a specific circuit other than the usual circuit. Japanese Unexamined Patent Application, First Publication, No. Hei 11-98871 discloses an example of such a technique.
However, in the conventional technique, if a leakage occurs at the coil terminal of the electromagnetic relay which is wet by water, current flows through the coil and the electromagnetic relay may not accurately operate. Therefore, in the above case of using a wet coil terminal of the electromagnetic relay, the electromagnetic relay may inaccurately operate regardless of whether it executes a sensor operation for detecting water leakage. In order to prevent such inaccurate operation, the electromagnetic relay and the circuit substrate may be sealed using a resin material or the like, but this causes a large increase in the necessary costs.
In consideration of the above circumstances, an objective of the present invention is to provide an electromagnetic relay and circuit substrate comprising the same for preventing erroneous operation when they are wet by water, at low cost.
Therefore, the present invention provides an electromagnetic relay comprising:
a case having fluid-tight characteristics;
an excitation coil provided in the case; and
electrodes connected to both ends of the excitation coil in a manner such that at least a portion of each electrode is formed outside the case and is exposed to an area where a liquid can penetrate.
Accordingly, when the electromagnetic relay is wet by or immersed in an electrically conductive liquid, a parallel circuit consisting of the excitation coil and an area between the electrodes is formed so as to prevent a current from flowing at the electromagnetic relay caused by a leakage current flowing through another portion. Therefore, erroneous operation caused by a leakage current can be prevented.
In the above basic structure, the electrodes may have a plate-like shape and closely face each other. Accordingly, an optimum resistance can be obtained by adjusting the area of the electrodes and the distance between the electrodes. In addition, if the electrodes are attached to an outside face of the case, it is possible to detect the penetration of liquid (such as water) before the liquid reaches the faces of the case. Therefore, erroneous operation can be prevented as quickly as possible.
Also in the above basic structure, the electrodes may have a plate-like shape, and may be arranged on the same plane and close to each other. Accordingly, an optimum resistance can be obtained by adjusting the area of the electrodes and the distance between the electrodes. In addition, if the electrodes are attached to an outside face of the case, the occupied space can be smaller. Therefore, a smaller device can be manufactured.
Also in the above basic structure, the electrodes may be attached to an outside face of the case. Accordingly, the electromagnetic relay efficiently functions as an assembly for preventing erroneous operation caused by the penetration of water or the like. Therefore, the flexibility for general use can be improved.
Also in the above basic structure, the electrodes may be insert-molded inside the case, and a portion of each electrode may be exposed outside the case. Accordingly, the electrodes can be inserted when the case is formed. Therefore, the manufacturing costs can be decreased in comparison with the case of attaching the electrodes after the assembly of each relevant part is finished.
Typically, when the area between the electrodes is immersed in an electrically conductive liquid, a leakage current flows between the electrodes. Accordingly, it is possible to prevent a current from flowing at the excitation coil side. Therefore, erroneous operation can be reliably prevented.
The present invention also provides a circuit substrate comprising an electromagnetic relay having any of the structures as explained above, wherein only one of the electrodes is provided at the electromagnetic relay side while the other is provided at the circuit substrate side. Accordingly, when the electrode at the electromagnetic relay side and the electrode at the circuit substrate side are immersed by an electrically conductive liquid, a leakage current can flow between the electrodes. Therefore, it is possible to prevent a current from flowing at the excitation coil side is such a case, thereby preventing erroneous operation of the electromagnetic relay.
The present invention also provides an electromagnetic relay comprising:
a case having fluid-tight characteristics; and
an excitation coil, provided in the case, having two coil terminals at both ends thereof, each coil terminal protruding outside the case, wherein one of the coil terminals functions as the earth side, and at least said earth-side coil terminal is shielded by a shield for preventing leakage from the earth-side coil terminal.
According to this structure, it is possible to prevent leakage from the coil terminal at the earth side by the shield. In addition, the electromagnetic relay having this structure can be manufactured only by adding the above shield to the conventional structure.
The present invention also provides an electromagnetic relay comprising:
a case having fluid-tight characteristics; and
an excitation coil, provided in the case, having two coil terminals at both ends thereof, each coil terminal protruding outside the case, wherein each protruding portion is bent and the portion beyond the bend is used as an electrode.
According to this structure, (plate-like) electrodes can be omitted, thereby decreasing the necessary costs.
Typically, the electromagnetic relay as explained above is used in a drive circuit for driving a motor for opening and closing a window of a power window apparatus of a vehicle. Accordingly, it is possible to prevent a problem in the operation of opening/closing a window provided in a vehicle door which tends to be penetrated by water or the like. Therefore, the reliability as a vehicle part can be improved.
The present invention also provides a circuit substrate comprising an electromagnetic relay as explained above. Accordingly, the measures for preventing erroneous operation caused by a penetrating liquid can be practiced at the electromagnetic relay side. Therefore, the reliability of the whole circuit substrate can be improved without limiting the kind of the circuit substrate.